Chlamydia trachomatis is a human pathogen that is responsible for a significant proportion of ocular and sexually transmitted diseases worldwide. Many of the consequences of the interaction between chlamydia and the host environment during the course of infection are thought to be directly related to the composition and arrangement of the surface of the chlamydial outer membrane. The objective of this proposal is to characterize the structure of the outer membrane of Chlamydia trachomatis. The primary focus will be on outer membrane (OM) proteins. the synthesis of OM proteins will be monitored during the developmental cycle by an immuno-electrophoretic transfer method using monoclonal antibodies to determine when and how many of these OM proteins are made. The location of proteins within the inclusion will be determined by immune electron microscopy using antibodies to determine if selected OM components are released in OM blebs by reticulate bodies (RB) during the reorganization into elementary bodies (EB). The arrangement of the major surface proteins of chlamydia, at different phases of the developmental cycle, will be determined by a nearest neighbor analysis using bifunctional protein cross-linking reagents. Such studies will define the evolution of protein-protein interactions during the developmental cycle which may provide a mechanism for the acquisition of pathogenic properties of EB, and possibly for some of the known biological differences among various chlamydial strains. The studies will be extended to determine the extent of natural disulfide bonding between molecules of the major outer membrane protein, and the role such bonding may play in the formation and the maintenance of OM structure. The long-term objective is to develop a model of chlamydial OM surface structure that can serve as a basis for further studies to determine the molecular basis of the pathogenesis of chlamydial infections.